The present invention relates to a method and apparatus for removing suspended matter from liquid. The method and apparatus of the present invention further relates to liquid-solids and/or liquid-liquid separation. More particularly, the present invention relates to a method and apparatus which separates suspended impurities from liquid through flotation of impurities using gas bubbles, followed by filtration of the liquid, within a single cell treatment vessel.
Multiple industries including oil, paper and pulp, textiles, electricity generating and food processing present an ever present and growing problem of contaminated liquids, especially water as a by product of the various processes; in particular, water produced in the oil and gas industry, and waste water streams in the paper and pulp industry. A method commonly used to separate oil and suspended material from water and other liquids is the gas flotation separator.
U.S. Pat. Nos. 5,080,802 and 5,156,745 provide single cell induced gas flotation separators. In practice these devices are often used in conjunction with wholly separate filtration systems. The filtration process is used to remove any impurities that remain in the liquid effluent of the flotation separator. A filtration process alone would often be inadequate to treat the liquid stream being treated by the flotation separator, but is effective in "polishing" the flotation separator effluent. However, use of a wholly separate filtration system can result in expensive and wasteful duplication of equipment. Two vessels may be required--one for floatation, and a second vessel for filtration. An additional pump or pumps may be required, to create adequate liquid flow through a wholly separate filtration system. Additional piping to connect the flotation device and filtration device is needed.
Many flotation separators are used in remote locations or in locations with severe space limitations. For example, use of flotation separators in the oil and gas industry, particularly on offshore production platforms, can be impacted by space limitations. Use of wholly separate filtration systems exacerbates such problems. Transportation of filtration equipment to remote locations and maintenance of such equipment adds expense to the liquid treatment process.
The present invention provides an apparatus and method for treating contaminated liquids using gas flotation followed by filtration in a single cell vessel. This approach resolves the problems inherent in the use of wholly separate filtration systems in conjunction with flotation separators. A single cell vessel houses both the flotation means and the filtration means employed in the present invention. Use of a single cell vessel not only reduces the space required for the flotation and filtration treatment equipment, but also reduces the total cost involved in obtaining, maintaining, and using such equipment, since duplication of equipment is eliminated.